Conventionally, azo pigments, pigments of C. I. No. 11710, 21090, 21100, 21095, 15630:1, 15585:1, 158501:1, etc., in particular, are widely used to color printing inks, coating compositions and plastics. However, the tinting strength, clearness and transparency of these pigments are inferior, and their fluidity in a vehicle is also poor. In order to improve the dispersibility of a pigment in a vehicle, a method is known which comprises treating the pigment with a rosin. However, this method involves a problem that the tinting strength is degraded. Further, another technique is known which comprises adding 0.1 to 50% by weight of a methyl-, carboxyl-, halogen atom- and/or nitro group-substituted diazo or coupler component into a diazo or coupler component. However, the resultant pigment has great drying and aggregation force and requires a considerably longer period of time to be dispersed in a vehicle, and a dispersion prepared therefrom also has a high viscosity.
Japanese Patent Laid-Open Publication No. 166266/1981 discloses a dispersant of an amine-based pigment derivative. This dispersant has a great effect on making a pigment fine and stabilizing it, and a dispersion prepared by dispersing a pigment in a vehicle by using this dispersant has a low viscosity and good storage stability. However, this dispersant can give no satisfactory quality of clearness and transparency.
U.S. Pat. No. 4,664,709, corresponding to Japanese Patent Laid-Open Publication No. 246260/1986, discloses a dispersant in which alkyl amine(s) such as tetramine, triamine, etc., is directly connected to a coloring matter. However, a dispersion formed by dispersing a pigment in a vehicle by using this dispersant causes a stain on hue, and fails to give satisfaction concerning dispersibility, gloss, concentration, viscosity, stability with time, etc.